Enclosure; Drive Units; Crossover - Bowers & Wilkins Nautilus User Manual

Enclosure

Exponential line loading is used for all four 0mm thick Glass Reinforced Plastic (GRP) has
drive units, primarily to achieve freedom from been used for the exterior surface which, when
resonance and reflection, but also for the coupled with the doubly curved shape, results
in an extremely stiff enclosure. The inner turns
damping effect on the fundamental resonance
in the low frequencies. of the spiral are bounded by a foam filled GRP
The two dome units are tightly coupled to which braces the opposite faces of the snail in
their respective wave guides via a hollow pole a manner similar to the Matrix type enclosure
magnet which causes minimal discontinuity to perfected by B&W.
the advancing wave front. The external form of the Nautilus has been
A hollow pole magnet is also to be found achieved using a blend of hand-built forming
behind the lower mid diaphragm supported by a and advanced CAD technology borrowed from
chassis which itself forms the first 50mm of the the automotive industry. This enables B&W to
wave guide. The tube to which this is attached is maintain mathematical accuracy of the wave
shaped to smooth the transition from the chassis. guide and to produce the final mould tool to
The distinctive natural appearance of Nautilus submillimetric accuracy.
is derived from the best compromise of folding The high gloss surface finish is the result
a tapered tube to save space whilst maintaining of using a two-part acrylic paint with a deep
the highest curvature-to-width ratio. Traditionally, lacquer coat for lustre and durability. A 50kg
folded pipes have involved many 80° bends block of polished terrazzo type material supports
which have serious frequency dependent the complete mollusc.
transmission properties.
6

Drive units

Crossover

Each drive unit has been developed to The division of the signal into the four required
operate as a piston within its intended bandwidths is accomplished in the Nautilus
frequency band, with two octaves between Active Crossover via totally nonresonant
the upper roll-off and the first sign of break- circuitry. Both inputs and outputs offer
up modes. Extensive use of aluminium in single and balanced operation, the latter
the diaphragms makes this possible. All being particularly useful in noisy electrical
voice coils are wound on polyimide formers environments, although a slight subjective
to eliminate eddy-current losses, which are improvement has been observed when
particularly serious at high frequencies. using balanced signal interconnections at
A 9.5kg (lbs) magnet with a 00mm every stage.
(in) voice coil acts as the massive motor of With suitable pre- and power amplifiers,
the 00mm (in) bass unit. This, when used one unit is required for each loudspeaker
in the exponential line enclosure, results in and should be sited close to the power
a high-pass behaviour so over-damped that amplifiers. A power supply connection for
the traditional second-order characteristic each crossover is required.
is replaced by two distinct first-order slopes
and no stored energy.
A 50 micron one-piece aluminium cone/
centre dome ensures coherent motion to
beyond .5kHz. From 0Hz to 880Hz,
a 00mm flat-fronted unit is employed to
prevent the gentle cavity resonance found
in conventional cone units at around kHz
interfering with the output from the upper
midrange unit. A rare earth magnet assembly
with hollow pole is used to minimise the
obstruction to the rear radiation from
the diaphragm.
Two domed units of anodised aluminium
of similar construction, 50mm and 5mm
in diameter, handle the 880Hz-.5kHz and
.5kHz-5kHz ranges respectively. All drive
units are completely mounted on silicone
rubber O-rings to decouple them from
the cabinet.
Important: your dealer must
check that the serial number
located at the rear of each
crossover unit matches that
of the loudspeaker – and that
the stated voltage is correct
for your mains supply.